Packaged magnetron

ABSTRACT

A packaged magnetron comprising a cylindrical permanent magnet coaxially disposed on the outer periphery of an anode, a radiator located between said magnet and anode, two circular conjugate yokes positioned on the magnet, facing each other, and a plurality of holes made in said yokes.

United States Patent Akihlro Fukatsu Yokohama;

Masao Kato, Tokyo, both of Japan Appl. No. 52,892

Filed July 7, 1970 Patented Oct. 19, 1971 Assignee Tokyo ShlbauraElectric Co. Ltd.

Kawasaki, Japan July 10, 1969 Japan 1 Inventors Priority PACKAGEDMAGNETRON 6 Clalms, 4 Drawlng Figs.

US. Cl 313/153,

313/l1,315/39.71 Int. Cl 1101] 25/50 [50] Field ofSearch 313/153,

' [56] References Cited UNITED STATES PATENTS 3,302,060 1/1967 Blok eta1 315/3911 FOREIGN PATENTS 1,041,518 9/1966 Great Britain 313/153Primary Examiner-John Kominski Attorney- Flynn & Frishauf ABSTRACT:A-packaged magnetron comprising a cylindrical permanent magnet coaxiallydisposed on the outer periphery of an anode, a radiator located betweensaid magnet and anode, two circular conjugate yokcs positioned on themag not, facing each other, and a plurality of holes made in said yokes.

PACKAGED MAGNETRON BACKGROUND OF THE. INVENTION This invention relatesto a packaged magnetron, particularly to a packaged magnetron withimproved yokes.

The conventional packaged magnetron used for a domestic microwaveheating apparatus consisted of two columned magnets disposed across amagnetron tube body, facing each other and two conjugate yokes, eachshaped like a square plate, mounted in contact with the upper and lowerends of the magnetron tube body and the magnets, respectively.

There was, however, a fear that the prior art magnetron had the magnetsoverheated by the heat generated by the magnetron tube body, thusdeteriorating its magnetic characteristics. For this reason, a castmagnet of a good temperature characteristic, though expensive, wasemployed. Since the magnet takes a major portion of the whole cost ofthe magnetron, use of an inexpensive magnet is desired. Indeed, aferrite magnet was inexpensive, but was inferior to the cast magnet intemperature characteristic; the magnetic force of the cast magnetdecreased by 0.02 percent per unit temperature 1' C. while that of theferrite magnet decreased by 0.2 percent. That is the reason why theinexpensive ferrite magnet was not so much used.

The magnetical properties of the cast magnet necessitate the elongationof a magnet and thus of a magnetron. For example, when this type ofmagnetron was mounted in a microwave cooking apparatus, the entireapparatus became too large. The magnetron is mounted on the mountingplate of oven of the cooking apparatus through the gasket. The gasket,however, having a poor heat conduction, is heated in the portions ofgreat field strength because of the ohmic loss due to the skin effect,thus losing the gasket effect and causing a spark in the gasket portion.This phenomenon cripples the magnetron by damaging the output domeglass, perforating the glass-scalable metal and lowering the degree ofvacuum by melting the brazing metal. Furthermore, the yoke should not betoo wide because of cooling. In order to pass the required fluxtherefore, it should be thick sufficiently. If the yoke were too thick,however, it would be pressed with difficulty.

SUMMARY OF THE INVENTION Accordingly, an object of this invention is tosurmount these disadvantages and provide a packaged magnetron employingan inexpensive ferrite magnet and capable of obtaining a continuouslyhigh output by forced gas cooling, comprising a pipe-shaped magnetcoaxially disposed with a spacing on the outer periphery of themagnetron tube body, two conjugate yokes mounted in close contact withthe two opening ends of the magnet respectively, so as to allow themagnetron tube body and magnet to be interposed therebetween, and aplurality of cooling holes radially disposed on the yokes.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a sectional view illustratinga magnetron embodying the present invention;

FIG. 2 is a plan view illustrating the magnetron of FIG. 1;

FIG. 3 is a sectional view illustrating another embodiment of theinvention; and

FIG. 4 is a sectional view of FIG. 3 taken along line IV-IV.

DETAILED DESCRIPTION OF THE INVENTION As shown in FIG. I, a cylindricalferrite magnet 11 is coaxially disposed with a spacing on the outerperiphery of a magnetron tube body 12. Two conjugate disc yokes l3 and14 are mounted in close contact with the both opening ends of the magnetll, respectively. Holes 15 and 16 are made in the centers of the discyokes l3 and 14, respectively. A cathode bushing 17 and an antennaportion 18 of the magnetron tube body 12 are projecting from the holes15 and 16, respectively. The magnet II and the magnetron tube body 12are fixedly disposed between the two yokes l3 and i4. Cooling holes l9and 20 are made at regular intervals in the circular direction in thesurface of the yokes l3 and 14 located over the spacing respectively.Cooling gas, such as air, passes through these cooling holes 19 and 20,respectively.

With this construction the magnetron of the invention has two conjugateyokes l3 and 14 disposed in close contact with the entire opening endsof the magnet 11, respectively. Thus the magnetic flux of the magnet 11passes in the line of the axis of the magnetron tube body-l2 throughalmost entire regions of the yokes l3 and 14, respectively. Theresultant substantial increase of the flux-passing region causes thecorresponding decrease of the yoke thickness, thereby facilitating thepressing of the yoke. The anode of the magnetron tube body 12 is heatedby the electrons emitted from the cathode and accelerated. However, thisheat escapes outwardly through a plurality of cooling holes 19 and 20made in the yokes 13 and 14 respectively, thereby preventing themagnetron tube body 12 from being overheated. The cooling effect of themagnetron can be enhanced by forced air cooling, thereby continuouslyobtaining a high output.

The effective cooling of the magnetron causes the magnet not tooverheat, therefore the magnetron permits employment of a ferrite magnetwhich is inexpensive through it may have bad temperaturecharacteristics. The flattening (i.e., giving a large coercive force)characteristic of the ferrite magnet can contribute to a decrease in theheight of the magnet 11 and thus of the entire magnetron. Furthermore,the ferrite magnet, which possesses the aforesaid characteristics isfree from any external effect arising during the replacement of amagnetron tube body, and eliminates the necessity of carrying outmagnetization as has been required for the prior art magnetron involvinga cast magnet, thus permitting the replacement of the tube body to beperformed simply by removing one of the conjugate yokes.

When this magnetron is mounted in an apparatus, such as microwavecooking apparatus it is disposed on the mounting plate at the openingend of the cylindrical magnet. The resultant large distance between theantenna portion 18 of the magnetron tube 12 and the mounting plateopposite to the yoke, such as the yoke l3, 14, 24 or 25 can prevent themagnetron tube body from the overheating damage due to plasma sparks,thereby preventing the damage of the antenna dome.

FIG. 3 illustrates another embodiment of the present invention. Aradiator 21 is coaxially disposed around the outer portion of themagnetron tube body 12 and a cylindrical magnet 11 is coaxially disposedaround the radiator 21. On both opening ends of the cylindrical magnet11 are respectively settled yokes 24 and 25 each of which has a circularedge portion 26 and a ring-shaped hollow projection 27 projectedcoaxially from the circular edge. The magnetron tube body 12 is fixedlyinterposed between the yokes 24 and 25, a cathode bushing 17 and antennaportion 18 projecting respectively from holes 22 and 23 bored in thecenter of the yokes. A plurality of cooling holes 28 and 29 are bored inthe surface of the projection of the yokes at regular intervals and tothe extent of both sides thereof.

The magnetron of this construction has a better cooling effect than theprevious embodiment due to the mounting of the radiator and asubstantial increase in the total areas of the cooling holes 28 and 29.The output can thus be so much increased. The shapes of the yokes 24 and25 are well adapted for passage of the flux from the magnet. The lessthe leakage of magnetic flux, the more effective use of the flux.

It will be understood that various changes and modifications may be madewithout departing from the spirit or scope of the invention hereindisclosed. It is intended, therefore, that all matter contained in theforegoing description and in the drawing is to be interpreted asillustrative only and not as limitative of the invention. For example,the cylindrical magnet previv ously described may be replaced by aplurality of curved magnets combined. The use of a magnet need not berestricted to that of a ferrite magnet, but any other type of magnet maybe employed.

What we claim is:

l. A packaged magnetron comprising a magnetron tube body, a pipe-shapedmagnet coaxially disposed with a spacing on the outer periphery of saidmagnetron tube body, two yokes closely fixed on the both sides of themagnet respectively, and a plurality of cooling holes radially disposedin those areas of each of said two yokes located over said spacing.

2. The magnetron as claimed in claim 1 wherein the magnet is a ferritemagnet.

3. The magnetron as claimed in claim 1 wherein the pipeshaped magnet isa cylindrical magnet and the two yokes are of the disc type.

4. The magnetron claimed in claim 1 wherein a radiator is coaxiallylocated around the magnetron tube body.

5. The magnetron as claimed in claim 1 wherein each of said two yokescomprises a circular edge portion and a ring-shaped 5 hollow projectionprojected coaxially from the circular edge portion.

6. The magnetron as claimed in claim 5 wherein each of said yokes has aplurality of cooling holes bored in the surface of the ring-shapedhollow projection at regular intervals and to the extent of both sidesthereof.

1. A packaged magnetron comprising a magnetron tube body, a pipe-shapedmagnet coaxially disposed with a spacing on the outer periphery of saidmagnetron tube body, two yokes closely fixed on the both sides of themagnet respectively, and a plurality of cooling holes radially disposedin those areas of each of said two yokes located over said spacing. 2.The magnetron as claimed in claim 1 wherein the magnet is a ferritemagnet.
 3. The magnetron as claimed in claim 1 wherein the pipe-shapedmagnet is a cylindrical magnet and the two yokes are of the disc type.4. The magnetron claimed in claim 1 wherein a radiator is coaxiallylocated around the magnetron tube body.
 5. The magnetron as claimed inclaim 1 wherein each of said two yokes comprises a circular edge portionand a ring-shaped hollow projection projected coaxially from thecircular edge portion.
 6. The magnetron as claimed in claim 5 whereineach of said yokes has a plurality of cooling holes bored in the surfaceof the ring-shaped hollow projection at regular intervals and to theextent of both sides thereof.